Frequency controlling system



Feb. 2, 1954 H. TUNICK 2,668,232

FREQUENCY CONTROLLING SYSTEM Filed May 15, 1945 3 Sheets-Sheet lINVENTCR. hA/aey 72//wc/ q ro e/yiy Feb. 2, 1954 H, u cK 2,668,232

FREQUENCY CONTROLLING SYSTEM Filed May 15, 1945 3 Sheets-Sheet 2 I N VEN TOR. #4:: y 7Z/N/c/c 7 Feb. 2, 1954 HITUNICK FREQUENCY CONTROLLINGSYSTEM 3 Sheets-Sheet 3 Filed May 15, 1945 Patented Feb. 2, 1954 UNITEDSTATES PATENT OFFICE 2,668,232 FREQUENGY CONTROLLING SYSTEM Hwy T nick,R e, poration oi'iiine a,

assignor to Radio Cora corporation of Delaware Application May 15, 1945,Serial No. 593,956 3 Claims. (01. 250-47) \e The object of my presentinvention i to vpma sharply resonant system. The response of this ystemis to produ e a wave wh ch reverses in phase a h mean frequency ofoperation of the oscillator undercont iol passes thr u h t e s nant fequency of the arp y resonant system- The wave of varying amp itud isdetected in an amplitude modulation detector and comb ned in a phasedetect r with Wav s of con tant r quency derived irom the c rol s urce.The o tput of the phas detec or is use o correct the frequen y oi the irouency modulated os llation specified o pr determined, that is adesired, 'me n frequency of operation. It will be noted, as will beexplained m r ul y .hereinaiter, that the controlling outp t of h phasede ctor i of variable amplitude zero when the m an freq ency of opration of the irequen y modu ated oscillato -is correct and reverses inpolarity whentne mean frequency of operation .of the frequency modulateos lla pas es throu h r chan es from on side to another of th desiredfrequency of operati As required by layv, y invention'is defined withparticularity the appended claims. However, its more detailed structuralorganization and mode of operation may better he understood by r ferringt he foll w ng m re detailed. sp ificaion together with the accompanyindrawing wherein:

Figure 1 illustrates the apulication oi present automatic frequencycon-trolling system to a transmitter employing successi e fr eueneymodulat ons;

Figure 2 is a modification Wheheill the transmitter employed radiates awave'newing a single signal frequency modulation;

Figure 3 illustrates heteroclyning' apparatus which may be used inconjunction with the system of Figure *2; 5

Figure ,4 illustrates the manner which a mead-electric crystal tankcircuit or filter may' be enerator so as c op rate at a ence is made tothe a i mew-c c e wa ehann p us and The latter is maintai ed atsubstituted for the vlow loss parallel tuned resonant tank circuit ofFigure '2; and

Figure 5 is a schematic block diagram of a radio receiving and relayingsystem useful in conjunction with the transmitting arrangement of Figure'1 and making use of the method and system of automatic frecuencycontrol involved ini'li ure 1.

Fi l I have illustrated schematicaiiy and in w rin dia ram iorm, anultra short wave frequency modulated transmitting system making use f myimproved automatic frequency con ollin arran ement. Si nals picked up by'mic oplione :2 a e amplified in audit) firs-fluency .plifiel" sand d toa sub-carrier frequency modue ion nerators. Th ou put for f equenoy modlated sul -c 'rier oscillator e may be a maX-imurnswing of m nus 196kiio ycles and this frequency modulated sub cerri r w e is resonated inthe tuned circuit 8, m de suit bly flat over the operating band ofrequencies :by r sistor it. For a fict on o oscillator s retessut- -carier enerating and qu n y m dulat n system 516.2, 4.25 and ion of Fig. lof the conch-ins .apnli ti, Thomp n! r l Number 5 6 53, filed Beloru-6, 1. .9 5, nowliatent No, 2,51sA 5 da-teddul 11, 1950 and also to themore specific wirin diagram and de cription application- The f u ymodula d sub carri it fe thr ugh unod irj t li' resistor 12 so as tohave a of Fig 4 of said Thom son vfi t frequency one epearing in circuit1 ii are tr-ode or plate electr de i of a re lex oscillato system is inorder to freguency modulate the high frequency wave output of oscillator18.

It W111 e noted that the reflex oscillator 18 makes use of ahermetically sealed c ntain r 2 hermetically sealed to a met c r s nator22 having a gap covered over by grid structures 24 and 2.6" vIt will beappreciat d that the cav ty resonator 221s in the ,form of a tcroid.

also within the container as are an electron 2 5 and the plate orreflect r {l V a negat ve potentia with respect to gr unds-y means of thond nse bypassed sour e of potential ,2?- The to oid is mainta ed a apos tive potential with respect suit bl b oaden d in a I toroid 22 isfed through 1 ductively coupled to the space within the toroid, 4 to asuitable radiating antenna 32.

' tank circuit 30. cross section, consists of an outer cylindricalmetallic conductor 38 and an inner "both mounted upon metal base 42.tially one-quarter wave length long at the operating frequency or mean 1of reflex oscillator l8.

' adjusted so that the pearing in the waves generated in toroid 22 hasto ground by I condenser 64 "for the radio frequency componentsappearing [in the output of crystal detector 50. Filter 6275 isconnected through by-r-pass condenser 205 to tively large amplitude aregenerated within the toroid. These waves have a frequency determined ingeneral by the tuning of the toroid, that is, the dimensions of thetoroid and also by the D. C. voltages applied at 28 to the toroid and at21 to the repeller electrode 15.

superimposition of the frequency modulated waves in circuit I0 on thevoltage from source- 21 will cause variation in voltage on the repellerelectrode l6, thereby causing frequency modulation of the waves withintoroid 22. These frequency modulated waves may have a mean frequency of,for example, 4,000 megacycles. By

:suitable adjustment of the coupling between tuned circuits 3 and It themaximum deviation .of the waves in tank 22 may be adjusted to be of theorder of plus and minus 2,000,000 cycles. A portion of the frequencymodulated waves in transmission line 30, in-

For automatic frequency controlling purposes --another portion of thewave energy in resonator 22 is taken by way of a transmission line 34,inductively coupled to the toroid 22 as shown,

and fed to a concentric line, low loss, high Q The latter, which isshown in conductor 40 and directly connected to a Inner conductor 40 issubstanfrequency of operation In order to maintain frequency stability,tank circuit 36, as before explained, is designed so as to be of verylow loss. Further it is mounted within a temperature controlled oven(not shown) for "maintaining the line at a substantially constanttemperature at which the line is resonant at the desired frequency ofoperation.

By means of a relatively low frequency oscillator 50 operating at, forexample, 1,000 cycles "and by means of transformer potentiometer 52,line 54 and 50, the repeller i0 is additionally modulated at 1,000cycles. 'Potentiometer 56 is 1,000 cycle modulation apa frequencydeviation such as plus and minus 25,000 cycles lying well within thefirst significant side bands produced by the action of oscillator 6 onthe high frequency output radiated over antenna 32.

In the output circuit of crystal detector 60,

I8 correthe resonant frequency of oscillations of higher frequency arefiltered 01f filter 02, it being noted that bypass is merely a highfrequency bypass constant amplitude phase and frequency derived fromsource 50 through transmission line I2, transformer 10 and potentiometer16.

Current flow in resistor I8 of the balanced phase detector systemincluding tubes 68 and 10, will act to impress across the terminals ofthe transmission line connected to resistor I8, a voltage which will bezero when the mean frequency of oscillator l8 corresponds to the res=onant frequency of tank circuit 35 and which will reverse in polarity asthe frequency of reflex oscillator l8 passes through the resonantfrequency of tank or concentric transmission line circuit 36. Hence, inthe event of drift of the mean frequency of oscillator 18 away from theresonant frequency of tank 30, a correcting voltage will be fed totransmission line 80 at its connection points to resistor 78. Thisvoltage is fed through reversing switch 82 to the resistor 84 in serieswith the plate supply lead 86. Switch 82 is thrown to that position forwhich the correcting voltage fed over line 00 to the resistor 84 in therepeller electrode Iii-cathode 25 circuit, brings the reflex oscillatorl8 back to a mean frequency of operation corresponding to the resonantfrequency of tank 36.

It will be noted that for the transmitting system shown in Fig. 1 areceiving arrangement will be required as described in the copendingapplication of Leland E. Thompson heretofore referred to. That is, inorder to derive the signal from wave radiated by antenna 32, successivefrequency demodulations are required. As a result of the first frequencydemodulation, the subcarrier appearing in circuit 8 will be reproducedas will also the 1,000 cycle controlling wave produced by generator 50.The latter, however, will immediately be filtered out by the followingtuned, sub-carrier frequency amplifying and limiting stages and will notappear in the final loud speaker output of the receiver.

In the event that the apparatus of Fig. 1 is to be used without thesub-carrier generator 6, then the output of audio frequency amplifier 4will be fed directly, by transformer action, into the lead 85. In thatevent, however, oscillator 50 should be designed so as to operate at asuperaudible frequency such as 30,000 cycles per second. This 30,000cycle wave will be reproduced in a receiver employing a single frequencydemodulation system. However, it will be filtered out in the audiofrequency stages of the receiver and thus will not be fed into theloudspeaker. In short, in the event that single frequency modulation isemployed in the transmitter, oscillator 50 should have a frequency aboveor below the extreme or limiting frequencies of the modulation band.

In the arrangement shown in Figure 2, a vacuum tube oscillator generator200 of the Hartley type is illustrated. This oscillator is provided witha tuned tank circuit 204, one end of which the plate of vacuum .end oftank circuit 204 is connected by way of push-push :to the plates of 5tube 200 and the other by-pass condenser 208 to the grid of tube 200.

The frequency of .oscillations appearing in tank circuit 204 is varied:by means of a reactance tube 2| 0 operating as a variable condenser inshunt to the tank circuit 204. That is to say, by virtue of the smallcondenser 232 having high capacitive reactance and the resistor 214having relatively low value. quadrature voltage from the plate circuitof tube 200 is impressedon the grid of tube 2| 0, .causing the latter to:draw a leading or capacitive current. The gain of tube 2 I0 is alsocontrolled by the output :of audio :frequency amplifier 2I-6 actuated bymicrophone 218 and coupled to the grid of reactance tube 210 throughtransformer 220 .and radio frequency choke coil 222. It will beunderstood, of course,

. that condensers 224 ancl226 are merely by-pass condensers. Thefrequency modulated output of oscillator .200 is fed :to frequencymultipliers :228,

power amplifier 230 and For automatic frequency part of the output oftank circuit 204 is fed through the inductive coupling link 234 to atemperature controlled tank circuit 236. The temperature controllingoven in which the tank radiating antenna 232.

. circuit 236 is mounted is indicated by the dotted lines 239. The tankcircuit :236 includes a coil 236 and a condenser 240., both coil 238 andcondenser 240 being of very low loss and sharply tuned to the desiredmean frequency or midfrequency of operation of oscillator 200.

- .As in connection with Figure l, the oscillator v200 is also frequencyaudible source 242 operating at, for example, 20 kc It is assumed thatthe upper frequency of the modulation band fed through the audiofrequency amplifier 2l-6 is, say, 10,000 or 12,000 cycles. ated bygenerator 242 are fed through potentiometer 244 and the secondary oftransformer 246 .in series with the voltages already present :in thegrid lead 248 for the grid of reactance tube 210. Potentiometer 244 isso adjusted that the deviation produced by the 20 kc. oscillator 242 inthe output of oscillator 200 is of a desirable value such as, forexample, plus and minus 5,000 cycles.

A part .of the wave energy appearing in the sharply tuned low loss tankcircuit 236 is picked 'pearing in circuit 258 will reverse in phase, de-

pending upon whether the midfrequencyof oscillator 200 is above or belowthe resonant frequency of tank 236. 'I'he fundamental frequency pickedup by circuit 25.8 is amplified in a suit- "able tuned amplifier .2 60which selectively passes the "waves of 20 k0,, but suppresses waves ofhigher frequencysuc'h as the second harmonic of 20 kc. generated'bygenerator 242. ,The output of amplifier 260 .is .fed throughconnections 262 and potentiometer 264 to the transformer .266. Thesecondary of transformer 2.66 feeds the output of connections 26.2cophaseally or in the balanced diode .detecting system 268, :27 0.Another portion of waves derived from generator 242 'is fed throughHconnections 212, potentiometer 21.4 and trans- :modulated by a super-Super-audible frequency waves gener- This frequency former 2 to tplates'oi the l nced di d phase detecting system 268, 270 in phaseopposition. As a result there appears across the output resistor 280,connected between the oa hodes of diodes 268, 5270 a voltage whichchanges in polarity as the frequency of operation of oscillator 200 goesfrom one side to another of the mean frequency of operation of tank 236.This voltage is fed through a manually operated reversing switch 282 toa resistor 284 in series with the grid Switch 252 should be thrown tothat position for which the voltage injected into resistor 264 is insuch direction as to cause the mean frequency of ope-rationof oscillator200 to come back to and correspond with the resonant :frequency of tank236. When the frequency of operation of tank 204 corresponds to therosenant frequency of tank 236 second harmonic voltages will be set upin the output .of diode 25.6, but these will be filtered oh" by theaction of circuit 258 and amplifier 260 so that no correcting voltageappears across the cathode resistor 280, thus allowing the oscillator200 to keep .on oscillating at the correct frequency.

.As shown in Figure 3,, if desired the link 234 may be broken at pointsa, a and b, b and the apparatus of Figure :3 connected therein. Theapparatus of Figure 3 consists of a converter or heterodyne detector 300fed with oscillations from a crystal controlled oscillation generator302. The intermediate frequency appearing in tuned circuit 304 is thenfed on .to the tank "236 which operates at the intermediate frequency.

may be made equal to the .difference in frequencies between the crystalcontrolled osciliator 302 and the desired mid-frequency of operation ofoscillator 200 or it may *be chosen as the sum of these two frequencies.

The apparatus of Figure 2, whether or not modified in accordance withFigure 3, may einploy a crystal instead of the tank circuitr236. Onemethod of making this substitution is shown in Figure 4. The link 234 isbroken at c, c and :the connections 252 are broken at d, d. The tankcircuit 236 and its couplings are removed and the apparatus of Figure 4connected in at points 0, c and d, d. It will be observed that theoscillations derived from the oscillator 200 are then fed to theelectrodes 400 of the crystal 402. The crystal 402 is provided with apair of output electrodes 404 connected to a suitable amplifier 406whose ou put is fed through the terminals d, d to the diode 256. "Theinput and output electrodes of crystal 402 are shielded from each otherby means of the grounded shields 406. Crystal 402 is ground foroperation at the desired mid-frequency of oscillator 200 or, in theevent that the heterodyning system of Figure 3 is employed, crystal 402would be ground to have a frequency corresponding to the desiredintermediate frequency or tuning of circuit 304. Also, when employingthe crystal arrangemen't'of Fig- 'ure 4, oscillator 242 maybe operatedat'sorhe sub audible frequency such as, for example, "10 cycles 'persecond.

In Figure '5 I have illustrated a combined rad-i0 receiving and relayingsystem making use of the automatic frequency controlling principleshe-retofore expounded upon in the descriptionof Figures 1 and 2.

lead 248 for rectance tube .210. V

also supplied with locally generated high frequency oscillations fromheterodyning generator or local oscillator 594. The intermediate ordifference frequency appearing in the output of converter 582 isamplified and limited in a series of intermedia.te frequency amplifiersand limiters -506; The output of limiters 505 is fed adiscriminator-detector system 588 such as described in the patent of S.W. Seeley, No. 2,121,103. In the output of discriminator-detector 583will appear the frequency modulated sub-carrier band of frequencies andalso the control wave, both of which it will be recalled had been usedto frequency modulate the final radiating oscillator or main carrieroscillator of the transmitting system of Figure 1. This control wav isan exact replica of and therefore corresponds in frequency to the waveoutput of oscillator 50 of Fig. l.

The band of sub-carrier frequencies appearing :in the output of detector598 of Fig. is filtered "out by a suitable filter 518 and amplified andlimited in amplifiers and limiters 5i2.

For relaying purposes the output of amplifiers .and limiters 512 is fedto a frequency modulated oscillation generator 5M operating at, forexample, a mean frequency of 5,000 megacycles and is deviated a maximumamount of, for example, :13 megacycles. The output of the frequency 1modulated oscillation generator 5M is fed to a suitable radiatingantenna 515 for relaying on to the next relaying or receiving point.

For local reception of the audio program or .modulating signal carriedby the waves received .upon antenna 550 of Fig. 5, a portion of theoutput of the amplifiers and limiters 522 is fed to a second frequencymodulation discriminator detector 518. In the output of thisdiscriminator, there will appear the original modulation band offrequencies. These are amplified by amplifier 522 and utilized in andtranslated by loudspeaker 522 or other signal translating device.

In order to maintain the output of converter 502 centrally located withreference to the pass band of intermediate frequency amplifier 508. a{portion of the output of amplifier 505 is fed as j shown to a low lossresonant circuit 524 sharply gtuned to the desired mid-frequency of theinter- -mediate frequency amplifier 5B5.

From what has been said heretofore. in connection with Figures 1 and 2,it should be evident that the output of circuit 524 will be an amplitudemodulated wave having a component in its modulation envelope having afrequency equal to the frequency of the control wave supplied byoscillator 50 of Fig. 1. This component reverses in phase as the mean oraverage frequency of the intermediate frequency output of 566 passesthrough the resonant frequency of low loss circuit 524. These componentsare detected in amplitude modulation detector 526 and filtered by filter528 tuned to pass waves of the control frequency to the phase detector536. Phase detector 535 is also fed with a control wave of invariablephase and substantially constant amplitude and frequency from thecontrol and tuned control wave amplifier 534. It will be noted thatfilter 532 derives its control wave or tone from the output 1. of thefirst frequency modulation discriminatordetector arrangement 5%.

In the output leads 53E of the phase detector 530, there will appear anautomatic frequency controlling voltage which is zero when theintermediate frequency output of converter 5G2 lies in the middle of thepass band of 5% tone or wave filter 532 "mean or average frequencyexactly in tune with low loss resonant circuit 524. However, the outputof phase detector 530 is of finite value and reverses in polarity as theintermediate frequency output of converter 582 becomes unsymmetricalwith respect to the resonant or mid-frequency of circuit 524. Thisautomatic frequency controlling voltage is fed over lines 536 to thelocal oscillation generator 5% in such a way as to bring theintermediate frequency output of converter 502 to a desired frequencyvalue.

It will be noted that a portion of the output of the oscillator 5M ofFig. 5 is fed through leads 538 to an automatic frequency controllingsystem 540. The frequency controlling system 540 is built in accordancewith the arrangement shown in Figure l and its output controllingvoltages are fed back over leads 542 to automatically correct thefrequency of operation of oscillation generator 5M. Also, it is to benoted that oscillator 584 is frequency modulated with a control tone .orwave fed to it over lines 542 connected to the .output of tone amplifier53. This will enable the use of my improved automatic frequencycontrolling system at the next receiving and relaying point. i

For a detailed description of the apparatus which I prefer to employ forthe oscillation generator 584. converter 582, intermediate frequencyamplifier 585 and oscillation generator 514 of Figure 5, reference ismade to the corresponding apparatus shown and described in theabovementioned patent to Leland E. Thompson. The hetercdyne oscillatorand converter are illustrated in detail in Figure 7 of the Thompsonapplication and the radiating frequency modulated oscillation generatoris shown in Figure 6 of that application.

The automatic frequency controlling system 540 of Figure 5 is the systemwhich I have described in connection with Figure 1 herein and,

- accordingly, it need not be described in detail.

In the arrangement of Figure l the control tone is labeled as a 1,000cycle tone. If desired, this control tone may be of any suitablefrequency and, in fact, may have a frequency of 60 cycles and be derivedfrom ordinary commercial power supply circuits.

In connection with Figure 2 it should be noted that the low lossresonant circuit need not be fed from the tank circuit'ZM of theoscillation generator but may, if desired, be fed from the output 7 ofthe power amplifier or from the output of one of the frequencymultiplier stages 228 of the transmitter. Obviously, in that event, thelow 7 loss resonant circuit is tuned or designed to have -a resonantfrequency equal to the desired frequency multiplied output of the masteroscillator.

If desired, the system of Figures 1 and 5 may be operated with allof theautomatic frequency .controlling apparatus located at the receivingterminal. Thus, the automatic frequency con- :trolling arrangement ofFigure 1, including the .resonant line 36, local control wave oscillator50 and the. phase detecting system involving tubes 68 and 10, could beomitted at the transmitting terminal and brought over to the receivingter- T minal of Figure 5 to automatically frequency conor has a"receiver.

' trol local generator 504 which may, of course, be

identical in construction to the reflex oscillator In that event, thecontrol tone from the control oscillator 50 now located at the Also, thelocal oscillation generator 504 would be frequency modulated with theoscillator 50. Low loss resonant circuit 524 would be resonant to adesired mid-frequency of the pass band of the I. F. amplifier 506.

Having claim is:

1. A transmitting arrangement for transmitting modulated high frequencyoscillations comprising, a source of signal waves, a source of waves ofsub carrier frequency, said sub carrier waves having a mean frequencyhigher than the highest frequency of the signaling waves; a modulatingcircuit for modulating the waves of sub carrier frequency with thesignal waves, a car rier frequency generator generating waves of afrequency suitable for transmission; a modulation circuit for modulatingthe waves generated by the carrier generator with the modulated subcarrier waves; a source of control waves of substantially invariablefrequency amplitude and phase connected to the carrier frequencygenerator for modulating the same in frequency; a low loss tank circuitcoupled to and excited by a portion of the frequency modulated waveoutput of the carrier generator said low loss circuit being tuned to afixed frequency; a detector connected to and detecting high frequencywaves flowing in said low loss circuit, the output circuit of saiddetector having therein waves of control frequency reversing in phase asthe frequency of the carrier shifts in frequency from one side toanother of a desired frequency of operation; a phase detector; circuitsfor applying to said phase detector said control waves of invariablefrequency and control waves derived from the output circuit of saiddetector; and a circuit utilizing voltages developed by said phasedetector to control the frequency of operation of said carrier frequencygenerator.

2. A frequency controlling system comprising, in combination, amicrowave oscillator having a reflector electrode, the frequency of thegenerated oscillations being variable in accordance with the potentialimpressed on said electrode, a resonant cavity tuned to a predetermineddesired ultra-high frequency of operation of said oscillator, means forsupplying oscillations from said oscillator through said cavity, asource of relatively low frequency control voltage waves, means forimpressing said control waves on said electrode, thereby tofrequency-modulate said oscillations, the amplitude of said controlwaves being sufficient to vary the frequency of said oscillations over arange extending on either side of said desired frequency, means todetect resultant amplitude modulation waves in the envelope of saidoscillations after transmission through said cavity, means to combinesaid control waves and thus described my invention, what I' saidmodulation waves and to derive a unidirectional potential therefrom,said potential having polarity and magnitude dependent upon deviationsin the mean frequency of said oscillations from said predeterminedfrequency, and means additionally to impress said potential on saidelectrode in a sense tending to maintain the mean frequency of saidoscillations at said predetermined frequency.

3. A frequency controlling system comprising, in combination, agenerator of high frequency oscillations having a potential-responsivefrequency control element, a resonant circuit tuned to a desiredoscillator frequency, means for supplying said oscillations through saidcircuit, a source of relatively low frequency waves having asubstantially constant amplitude, means for supplying said waves to saidcontrol element, thereby to frequency-modulate said oscillations over apredetermined frequency band, the amplitude of said control waves beingsuiiicient to vary the frequency of said oscillations over a rangeextending on either side of said desired frequency, means to detectresultant amplitude modulation waves in the envelope of saidoscillations after transmission through said circuit, means to combinesaid low frequency and modulation waves and to develop a unidirectionalcontrol potential therefrom, said potential having polarity andmagnitude dependent upon deviations in the mean frequency of saidoscillations from said desired frequency, and means additionally toimpress said potential on said element in a sense to oppose saiddeviations.

HARRY TUNICK.

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